In recent years, a significant industry has developed which involves the application of customer-selected designs, messages, illustrations, and the like (referred to collectively hereinafter as “customer-selected graphics”) on articles of clothing, such as T-shirts, sweat shirts, and the like. These customer-selected graphics typically are commercially available products tailored for a specific end-use and are printed on a release or transfer paper. The graphics are transferred to the article of clothing by means of heat and pressure, after which the release or transfer paper is removed.
Heat transfer papers having an enhanced receptivity for images made by wax-based crayons, thermal printer ribbons, ink-jet printers, and impact ribbon or dot-matrix printers, are well known in the art. Typically, a heat transfer material comprises a cellulosic base sheet and an image-receptive coating on a surface of the base sheet. The image-receptive coating usually contains one or more film-forming polymeric binders, as well as, other additives to improve the transferability and printability of the coating. Other heat transfer materials comprise a cellulosic base sheet and an image-receptive coating, wherein the image-receptive coating is formed by melt extrusion or by laminating a film to the base sheet. The surface of the coating or film may then be roughened by, for example, passing the coated base sheet through an embossing roll.
Much effort has been directed at generally improving the transferability of an image-bearing laminate (coating) to a substrate. For example, an improved cold-peelable heat transfer material has been described in U.S. Pat. No. 5,798,179, which allows removal of the base sheet immediately after transfer of the image-bearing laminate (“hot peelable heat transfer material”) or some time thereafter when the laminate has cooled (“cold peelable heat transfer material”). Moreover, additional effort has been directed to improving the crack resistance and washability of the transferred laminate. The transferred laminate must be able to withstand multiple wash cycles and normal “wear and tear” without cracking or fading.
Various techniques have been used in an attempt to improve the overall quality of the transferred laminate and the article of clothing containing the same. For example, plasticizers and coating additives have been added to coatings of heat transfer materials to improve the crack resistance and washability of image-bearing laminates on articles of clothing.
When imaging a dark substrate, an opaque light colored or white background is required to mask the dark background. This masking requirement presents a new challenge as coatings must be very opaque to be effective. The opacity can be achieved by use of pigment particles which are designed to scatter light, such as titanium dioxide particles ground to about 0.5 microns. However, the pigment concentration in coatings designed for heat transfer is limited since the pigments adversely effect the ability of the film to melt and bond to the fabric. They also stiffen the film and make it less durable to washing. One can simply employ a very thick film with more moderate amounts of pigment loading but the transfers made with these products are very stiff and uncomfortable.
Another problem with dark fabric transfers is that the colored graphics can penetrate into the opaque layer. This results in a decrease in brightness of the transfer, making it appear “chalky” or “washed out.”
A very similar problem to the dulling of images due to penetration into the opaque layer can occur in carrying out transfers to white or light colored fabrics. Penetration of the image into the fabric can make the image less vivid. Although it is possible to construct coatings which will not melt and flow significantly so that the image remains on the fabric surface, such coatings may not bond well to the fabrics. This results in cracking and peeling of the coatings in use or when they are washed.